Flotation of ores using addition polymers as depressants



States FLOTATION F ORES USlNG ADDITION POLY- MERS AS DEPRESSANTS No Drawing. Application April 7, 1953, Serial No. 347,414

14 Claims. (Cl. 209-166) This invention relates to froth flotation and more particularly to the flotation of ores having ganguc slimes.

Many ores have finely-divided gangue constituents present as slimes which interfere with flotation of the desired mineral values. The presence of gangue or slimy materials creates difiiculties in flotation by reason of contamination of the concentrate by the gangue or by the action of the gangue on the mineral values which prevents their flotation and hence reduces recoveries. In some ores the slimes are present as ordinary gangue minerals of a siliceous nature, while in other ores a carbonaceous gangue is present. While it is often possible to deslime ores prior to froth flotation, this is not always possible because in many cases certain components of the gangue carrywith them recoverable values and in other cases it is often necessary to grind the feed to such a very fine size that practically all of the feed may be considered as a slime.

In the past, dextrin, sodium silicate, glue and other organic protective colloids have commonly been used for the depression of gaugue during flotation. These colloids are frequently deflocculating agents and function to keep the slimy gangues in a highly dispersed state so as not to interfere with the flotation of the mineral values. Such colloids, while in widespread use, are not completely satisfactory, however, because they frequently cause the depression of certain of the desirable constituents of the ore as Well as the gangue and hence decrease recoveries of the valuable mineral values.

In accordance with the present invention, it has been found that froth flotation of ores is greatly improved when it is carried out in the presence as a gangue depressant of water-soluble anionic, linear, addition polymers of a monoethylenically unsaturated compound, and Water soluble salts thereof, having an average molecular weight of at least 10,000.

It is a surprising feature of the present invention that the linear, addition polymers and salts act as selective depressants for the gangue slimes without depressing to any appreciable extent, and thus preventing the recovery of, the desired mineral values. In making a choice between optimum grade and maximum recovery, slight losses in recovery are taken occasionally but in such cases the economic advantages of the high concentrate grade far outweigh the losses of recovery. Losses incurred by the use of the polymers of the present invention are considerably less than with ganguc depressants in use atthe present time.

It is a further surprising feature of the present inven- -tion that the linear, addition polymers work so effectively 'in depressing gangue during flotation because the mineral dressing art has heretofore considered that the slimes must generally be in a highly dispersed condition or otherwise the desired separation could not take place. In the practice of the present invention, however, these polymers which when used in the soil conditioning art are known to be strong flocculants for surface soils, have been found to produce remarkable results in depressing gangue during atent Q "ice flotation by a mechanism which is not clearly understood but the net result of which appears to be directly contrary to that which was heretofore considered to be necessary in the mineral dressing field, namely, a dispersed condition of the slimes. It is an observable fact, however, that by the use of the polymers or salts of the present invention, greatly improved metallurgical results are obtained on many ores with resultant improvement in concentrate grades and in many cases with added mineral recovery apparently by reason of the fact that the interfering gangue slimes which hinder flotation of the desired mineral values are effectively depressed.

It is an advantage of the present invention that it is applicable to gangue slimes of the most varied types of ores such as siliceous gangue present in metallic or sulfide ores, for example, lead, zinc, copper, pyrite, lead-zinc ores, precious metal ores, etc. It is also applicable to the various gangues present in non-metallic ores such as, for example, those of tungsten, manganese, barite, fluorspar, limestone and phosphate rock. Talcs, micas, clays, sericites, limonites, fine carbon and on occasion fine calcite are examples of gangues which interfere with flotation especially when these are present as slimes, and other minerals when in the form of slimes frequently are harmful.

It is a further advantage of the present invention that the linear, addition polymers or salts may be added at any convenient point in the ore treatment operation. Thus, for example, they may be introduced prior to and/or during the flotation operation. The point at which they are introduced may frequently depend on the particular ore being floated. Good results have been obtained when the polymers have been added to the grinding operation or to the conditioning step prior to flotation. In other cases, the polymers have been introduced into flotation circuits at the start and/or during flotation operations. Stage feeding during flotation has been very effective.

.The polymers are generally fed as solutions but may be added in dry form or as concentrated gels, if so desired.

Examples of water-soluble, anionic, linear, addition polymers of a monoethylenically unsaturated compound are polymers of unsaturated aliphatic monocarboxylic acids, such as acrylic acid, methacrylic acid, vinyl acetic acid, etc., and water-soluble salts thereof. These polymers may be obtained by polymerizing the acid itself or by polymerizing derivatives having groups which are hydrolyzable to acids, such as, for example, acrylonitrile, acrylamide, esters of acrylic and methacrylic acid, etc. The unsaturated monocarboxylic acids may be polymerized by themselves to form homopolymers or they may be copolymerized with compounds such as vinyl pyridine, vinyl acetate, styrene, vinyl ethers, vinyl halides, or even unsaturated hydrocarbons such as isobutylene. Polymers of polybasic unsaturated acids are also included, although here it is diflicult to obtain a homopolymer. For example, maleic anhydride itself will not polymerize, but it copolymerizes readily with such materials as styrene, vinyl acetate, acrylates and the like.

Among the various polymers and water-soluble salts thereof useful in the practice of the present invention are hydrolyzed polyacrylonitrile, polyacrylamide, polyacrylic acid, /2 calcium salt of hydrolyzed 1:1 copolymer of -vinyl acetate-maleic anhydride, hydrolyzed styrene-maleic mer, isobutylene-rnaleic anhydride copolymer, styrenemaleic anhydride copolymer, ethyl acrylate-maleic anhydride copolymer, vinyl chloride-maleic anhydride copolymer, hydrolyzed acrylonitrile-vinyl acetate copolymer, hydrolyzed acrylonitriie-methacrylonitrile copolymer, hydrolyzed acrylonitrile-methacrylonitrile-vinyl acetate terpolymer, hydrolyzed acrylonitrile-methacrylic acid'co'polyrner, vinyl pyridine-acrylonitrile copolymer, etc.

Among the best linear, addition polymers are those which are obtained by hydrolyzing'polymeric material containing polyacrylonitrile. These compoundsare'cheap and give ex'cellentresttlts. Here again, the polymer 'may be a 'hornopolymer or the acrylonitrile may be copolymerized with small amounts of othermaterials; suchas vinyl pyridine, acrylic esters and'the like; It'should be n'oted'that the products obtained by hydrolyzing' polymers such-as polyacrylonitriles are not completely identicalwith the corresponding polymers obtained by poly rnerizing acrylic acid. Both types are, however, useful in the present invention.

It'is'an'advantage of the present inventionthat the preferred type of linear, addition polymers; namely, hydrolyzed polyacrylonitriles, maybe of very low grade. It is thuspossible to use polyacrylonitriles which have insufiicientpurity for other uses, such as fibers, to prepare the polyacrylic acid of the present invention. The possibility of using these normally discarded, oft-grade'products makes a source of very cheap material availablefor use in the-present invention. Where the amount of byproducnofi gr'ade material is not sufiicient to supply the demand and the linear polymers must be made directly,

it is usually found that the homopolymer of acrylonitrile is somewhat cheaper to make than the copolymers The water-soluble polymers and water-soluble salts thereof as described hereinabove may be added to the ores being floated in amounts ranging from 0.001 lb. ton to 1.0 lb. ton but it has been found that with most ores optimum results are obtained by the'usc of 0.01 lb./ton to 0.2 lb./ tOn'.

Fo'r'o'ptimum beneficial effect, the molecular weightof the linear, addition polymer is of some importance in selectively depressing the gangue constituents of the ores. Itappears that the molecular weight should be at least about 10,000 in order to secure the desired results. The upper molecular weight limit does not appear to be at all critical and is set only by the practical difiiculty of making extremely highly polymerized polymers. Polymers having molecular weights ranging upward to about 500,000 appear to be quite satisfactory in the practice of the present invention. Those polymers having molecular weights much in excess of 500,000 are difficult to get into solution or to form dispersions thereof in water. Thus, theinsoluble ornon-dispersible polymers are not included herein. water-dispersible it is operable in carrying outthe present invention.

It is to be understood that since the herein-described polymers and salts serve solely as depressing agents for the interfering" slimes, a suitable mineral collector must be used in the frothfiotation process. The choice of pro moteifisnbt critical and is dictated solely by the mineral which is desired to be floated. Thus, suitable anionic prornotets such as the xanthates, dithiophosphates, naphthenic acids, fatty acids, resin acids and mixtures thereof, the alkali s'oaps' of such acids and their mixtures may be suitably'e'mployed. Cationic reagents such as longchain amines and amine derivatives may suitably be employed when the ore being treated is of the type that responds to such agents. Hydrocarbon oils and frothers such as pine o'il, cresylic acids, higher alcohols and other frothing' agents may also be used.

The invention will be described in greater detail in conjunction with the following specific examplesin which the parts are by weight unless otherwise specified.

However, so long as the polymer is wateror 1.2. Example 1 A sulfide lead-zinc ore containing 3.7% Pb and 6.0% Zn in a siliceous gangue was ground to 20% plus 200 mesh in the presence of 0.25 lb. per ton of sodium cyanide and 1.5 lb. per ton zinc sulfate. The resulting pulp was diluted to about 22% solids and conditioned.with.-0.l0.lb.per ton ammonium dicresyl dithiophosphate and 0i05"lb; p'er ton of a higher alcohol frother. The lead sulfides were then floated off to produce a concentrate which-assayed 24.75% Pb and 4.59% Zn and contained 98.2% :of the total lead and 10.5% of the total zinc. Thetailingfrom the lead flotation was conditioned with. 2.5. lb. per ton lime, 1.0 lb. per ton copper sulfate'and 0.1 lb. per ton technical sodium diisopropyl dithiophosphate and 0.05 lb. per ton of a higher alcohol frother. The-tailing was then iioated to remove zinc, producing a concentrate assaying 0.36% Pb and 39.8% Znand containing 1.2% ofrthe total lead and 79.7% of the total zinc. The-final flotation tailing assayed 0.03% Pb andv 0.86% Zn.

Asimilar test was. conducted. on thisorc using. 0.1111). per ton. ofthe sodium salt of hydrolyzed polyacrylonitrile, which was. added to the grinding operation. In the lead float, the concentrate assayed 31.41% Pb and.3.94% Zn andcontained 98.5% of the total lead and. 7.8% ofthe total zinc. The zinc concentrate contained 0.25% Pb and 39.79% Zn and contained 1.1% of the total lead. and 90.4% of. the total zinc. The flotation tailings contained 0.02% Pb and 0.14% Zn.

Theresults of these tests indicate that the useofthe polymer effected'a considerable improvement in the-grade ofthe lead concentrate without loss of recovery oflead, a decrease in the zinc losses into the lead concentrate and a marked improvement in. the zinc recovery.

Example 2 Flotation tests were conducted on a gold bearing pyrite ore containing 0.5 02. Au per ton. This ore which contained a feldspar-granite gangue was ground to 2.4% meshand floated with 0.1 pound per ton sodium secondary butyI xanthate and 0.1 pound per ton of a 1:1 mixture. of pine oil and a higher alcohol as frother. The metal lurgical results are given in the following table. In the first test, no polymer was used. In the next 3 tests, the sodium salt of hydrolyzed polyacrylonitrile was used in amounts ranging from 0.01 to 0.10 lb. per ton.

Percent Distributton Au Assay, Oz. Au/ton Test 1:

Concentrate Telling Test, 2:

Concentrate T iliu a g Test 3:

}1 none Hm Wm :19 ar 4 Concentrate Telling Hm P res The use of the polymer gave improved concentrate grade without causing gold losses.

Example 3 5 lead was recovered in a concentrate assaying 57.8% Pb. The flotation tailing in this test contained 0.35% Pb.

The use of the polymer in this test resulted in a higher recovery of lead in the flotation concentrate. This flotation feed contained a portion of its lead values as slimed lead sulfides and it will be noted that such values were not depressed by the use of the polymer, a factor which illustrates the selective action of these materials as gangue modifiers.

Example 4 A sulfide zinc ore from the southeastern part of the United States was ground at 60% solids, diluted to about 20% solids and conditioned with 0.5 lb. per ton of copper sulfate, 0.025 lb. per ton technical sodium diisopropyl dithiophosphate and 0.12 lb. per ton pine oil. The zinc was then floated off as a concentrate assaying 41.7% Zn and containing 96.1% of the total zinc contained in the ore.

In a second test on this ore, 0.1 lb. per ton of the sodium salt of hydrolyzed polyacrylonitrile was added after conditioning with the promoter-frother combination described above. Flotation of the zinc resulted in a concentrate assaying 42.1% Zn and containing 98.2% of the total 21116.

As in the foregoing examples improved metallurgy was also obtained in the treatment of this zinc ore.

Example 5 A sample of porphyry copper ore (0.8% Cu) was ground to minus 65 mesh in the presence of 0.1 lb. per ton of the sodium salt of hydrolyzed polyacrylonitrile, 1.5 lb. per ton lime, 0.04 lb. per ton technical sodium disecondary butyl dithiophosphate and 0.075 lb. per ton of higher alcohol frother. The ore was floated to produce a copper concentrate which assayed 22.1% Cu and contained 80.0% of the total copper. In a control test in which the polymer was omitted from the grind, a copper concentrate was produced which assayed 14.2% copper and contained 80.3% of the total copper in the ore. The main diluent in the copper concentrate in this test was fine gangue minerals.

It will be noted that a marked increase in concentrate grade was effected by the use of the polymer and that this was attained with essentially no loss in copper recovery. In certain other copper ores it is possible to use relatively large amounts of polymer, e. g. in the range of 0.75-1.0 lb./ton, without causing depression of copper values.

Example 6 A second copper ore similar to that used in Example 5 Was also treated with 0.1 lb./ton of various polymers and water-soluble salts and the above-mentioned lime-frother dithiophosphate combination in a series of separate tests and floated to produce a copper concentrate. The polymers used together with the recovery of copper and concentrate grade in each test are listed 1n the following table:

Concentrate, Percent Cu Polymer Used Assay Recovery None l5. 2 83. 4 Guanidine salt of hydrolyzed polyacrylonitrile 20. 7 83. 9 Diethanol amine salt of hydrolyzed poly- 24. 6 82.

aorylonitrile. l Sodium salt of 1:1 copolymer of vinyl oce- 22.4 82.0

tatemaleic anhydride. Polyacrylic acid 22.1 83.0 14 Calcium salt of vinyl acetaterneleic 23.1 82.6

anhydride copolymer. Polyacrylamide 23. 2 82. 2 Am?101l1illm salt of hydrolyzed polyacrylo- 23. 9 82.1

m r1 e. Hydrolyzed styrene-maleic anhydride co- 20.3 83. 0

polymer. Sulfonated polystyrene 18. 3 82. 8 Sodium salt of copolymer of vinyl methyl 21. 5 83. 5

ethermaleic acid. Ethyl aorylate-ammonium maleate 21. 8 82. 4 Styreneammonium maleate 19. 8 83. 1

6 The marked improvement in the grades of the copper concentrates obtained in the treatment of this ore outweighs the indicated slight losses in recovery.

Example 7 A tungsten ore in which various tungsten minerals were associated with a siliceous gangue was ground to pass mesh. This ore contained 0.9% W03. The pulp, after grinding, was conditioned with 5.0 lb. per ton sodium silicate, 8.0 lb. per ton sodium carbonate, 0.15 lb. per ton quebracho, 1.5 lb. per ton sodium resinate, and 1.2 1b.

Example 8 A tungsten ore (0.4% W03) containing various tungsten materials and a gangue composed of garnet, limonite, calcite, and silicate minerals Was ground to minus 65 mesh and conditioned with 0.04 lb. per ton of the sodium salt of hydrolyzed polyacrylonitrile, 4.25 lb. sodium silicate, 12.5 lb. per ton of soda ash, 0.2 lb. per ton quebracho, 1.0 lb. per ton sodium resinate and 0.5 lb. per ton oleic acid. The pulp was floated to remove a tungsten concentrate which was subjected to cleaning by reiiotation. A final concentrate was produced which contained 83.1% of the total tungsten. The tungsten content of this concentrate was 37.6% W03. A control tcst'on this ore was also conducted, in which the polymer was omitted. In this test a low grade tungsten concentrate resulted, which assayed only 5.5% W03. These test results illustrate the marked effect of the polymer on improving the grade of the tungsten concentrate.

Example 9 The tungstenore described in Example 7 was employed in a series of comparative tests with various polymers. The reagents and testing methods were similar to those outlined in Example 7. The polymers used together with the tungsten recoveries and concentrate grades are given in the following table:

A marked increase in concentrate grade was efiected by the use of the polymers.

Example 10 A Michigan iron ore containing hematite in a quartz gangue was ground to minus 65 mesh, diluted to about 25% solids and deslimed incompletely in the presence of 0.5 lb. per ton sodium silicate. The deslimed pulp was conditioned with 0.02 lb. per ton of the sodium salt of hydrolyzed polyacrylonitrile and 0.75 lb. per ton low rosin tall oil fatty acids, and then floated to produce an iron concentrate. This concentrate was then subjected to two cleanings by reflotation. The final concentrate contained 80.3% of the iron and assayed 64.9% Fe and 5.6% SiOa.

Example 11 A barite ore containing barite associated with quartz and iron oxides was ground to about 50% minus 200 meslr and-conditioned with 0.02 lb; per-touofthe'sodium salt'of hydrolyzedpolyacrylonitrile, 3.9 lb. per ton sodium silicate, 2.8 lb: per-"ton of'oil-soluble petroleum sulfonate and 0.06 lb. per ton of a seven carbon atom alcohol frother. A barite concentrate was then removed by flotation. 95.3% of the barite was removed. in this concentrate which contained'98.9% B21304.

Example 12 A Montana manganese ore containing about 17% Mn as rhodochrosite in a silicate gangue was ground and floated in the presence of 0.5 lb. per toncautic soda, 1.5 lb. per ton. sodium silicate, 1.2 lb. per ton oil-soluble petroleum sulfonate, 0.9 lb. per ton saponified cottonseed foots, and 0.005 lb. per ton of the sodium saltof hydrolyzed polyacrylonitrile. A manganese concentrate was removed containing 38.1% Mn. The recovery of manganese in' this concentrate was 94.6%.

Example 13 Flotation tests were also conducted on Canadian fluorite ore, which contained fluorite, calcite, feldspar, and small amounts of sulfide and oxide iron minerals. This ore contained about 27% CaFz. The ore was ground to about 45% minus 200 mesh, conditioned with 0.015 lb. per'ton of the sodium salt of hydrolyzed polyacrylonitrile, 0.25 lb; per ton quebracho, 3.0 lb. per ton sodium silicate and 1.0 lb. per ton oleic acid and floated to remove a fluorite concentrate. 82.1% of the fluorite was recovered in a concentrate assaying 98.1% CaFz.

Example 14 A Pennsylvania cement rock containing calcium carbonate in a gangue composed of quartz, sericite and carbon was ground to about 95% minus 200 mesh, diluted to 22% solids and floated-in thepresence of 1.0 lb. per ton crude calcium lignin sult'onate, 0.02 lb. per ton of the sodium saltof hydrolyzed polyacrylonitrile, 0.12 lb. per ton of higher alcohol frother and-0.7 6 lb. per ton vegetable fatty acid foots. The oleic acid promoter and frother were added in stages over an eight minute float; From a feed assaying 70.5% CaCOs, a concentrate was produced which assayed 78.1% CaCOs and contained 97.8% of the total calcium carbonate.

Example 15 A sample of Florida phosphate rock typical of material treated by flotation was deslimed and conditioned at 60% solids with 0.6 lb. per ton tall oil, 3.0 lb. per ton fuel oil, 0.4 lb. per ton caustic soda and 0.015 lb. per

tonof the sodium salt of hydrolyzed polyacrylonitrile,

diluted to about 20% solids and floated to produce a phosphate concentrate. From a flotation feed assaying about 32.9% bone phosphate of lime (BPL), a concentrate was produced which was cleaned twice. The final concentrate contained 72.3% BPL and 7.8% insoluble.

This concentrate represented a phosphate recovery of 79.6%.

Example 16 Example 17 The various polymer products herein-described are also useful as modifying agents when used with cationic collectors. The-furtherbeneficiation by flotation-etaphos- 20% solids and conditioned with 0.02 lb. per tonof the sodium salt of hydrolyzed polyacrylonitrile, 0.20 lb. per ton of tallow amine acetate, 0.12 lb. per ton of higher alcohol frother and 0.25 lb. per ton of kerosene and float ed to remove silica. Thesilica content of the original flotation. concentrate was reduced to 3.1% and, a weight recovery of phosphate of 90.89% was obtained. The phosphate content of the phosphate concentrate. was 73.5%.

We claim:

1. The method ofconcentrating orescontaining gangue slimes which comprises subjecting an aqueous. pulp, of saidoreto froth flotation in the presence of a collector and in the presence as a gangue depressant of water.- soluble, anionic, linear, addition polymers of a polymerizable monoethylenically unsaturated compound having an average molecular weight of at least 10,000 and being present inan amount sufficient to depress substantially said gangue slimes.

2. The method according to claim 1 wherein the polymeric materialv is present to the extent of from about 0.001 lb;/ton-to about 1.0 lbJtonby weight.

3. The methodaccording to claim 2 wherein the polymericmaterial is a polyacrylic acid. 1

4. The methodaccorcling to claim 2 wherein the polymeric material'is a polyacrylamide.

5. The method of concentrating orescontaining gangue slimes which comprises subjecting an aqueous pulpof said oreto froth. flotation in the presence of a. collector and inthe presence as a gangue depressant of a watersoluble salt of anionic, linear, addition polymers of a polymerizable monoethylenically unsaturated compound having an average molecular weight of at least 10,000 and being present in an amount sufficient to depress substantially' said. gangue slimes.

6. The method according to claimS wherein the polymeric material is present to the extent of from about 0.001 lb./ton to about 1.0 lb./ton by weight.

7'. The method according to claim 6 wherein the polymeric material is a sodium Salt of a hydrolized polymer of acrylonitrile.

8. The method. according to claim 6 wherein the polymeric material is a calcium salt of a hydrolyzedcopolymer of vinyl acetate and maleic anhydride.

9. The method according to claim 2 wherein the ore floated is a metallic ore.

10. The method according to claim 9 wherein the metallic ore is a sulfide ore.

11. The method according to claim 9 wherein the metallic ore is a copper ore.

12. The method according to. claim 9' wherein the metallic ore is a zinc ore.

13. The method according to claim 2 wherein the ore floated is a non-metallic ore.

14. The method according, to claim 13 wherein the non-metallieore is a tungsten ore.

References Cited inthefile of. this patent UNITED STATES PATENTS 1,976,679 Fikentscher et al. Oct. 9, 1934 2,211,686 Booth Aug. 13, 1940 2,229,272 Booth Ian. 21-, 19.41 2,341,046 Kirby Feb. 8',- 1944 2,497,863 Clemmer et a1 Feb. 21, 1950 

1. THE METHOD OF CONCENTRATING ORES CONTAINING GANGUE SLIMES WHICH COMPRISES SUBJECTING AN AQUEOUS PULP OF SAID ORE TO FROTH FLOTATION IN THE PRESENCE OF A COLLECTOR AND IN THE PRESENCE AS A GANGUE DEPRESSANT OF WATERSOLUBLE, ANIONIC, LINEAR, ADDITION POLYMERS OF A POLYMERIZABLE MONOETHYLENICALLY UNSATURATED COMPOUND HAVING AN AVERAGE MOLECULAR WEIGHT OF AT LEAST 10,000 AND BEING PRESENT IN AN AMOUNT SUFFICIENT TO DEPRESS SUBSTANTIALLY SAID GANGUE SLIMES. 